1. Field of the Invention
This invention relates to an insolation sensor for detecting an insolation receiving direction.
2. Description of the Related Art
Incidence of solar rays into the inside of a car where air conditioning is being utilized in the car, etc., is unavoidable. Therefore, to enable air conditioning control that takes into consideration the temperature rise resulting from the incidence of solar rays into the car, it has been customary to detect an insolation quantity and to correct and control a blow-out quantity of air and an air flow rate of an air conditioner in accordance with the detected insolation quantity.
Comfort inside the air conditioning space has been increasing in recent years, and attempts have been made to detect an incident direction of solar rays and to control air conditioning inside a car with good balance on the basis of the detection result in order to more finely control air conditioning.
A sensor for detecting the insolation direction of the solar rays is described, for example, in Japanese Unexamined Patent Publication (Kokai) No. 56-64611. According to this prior art technique, the solar rays are concentrated into a spot beam through a pin-hole and are then allowed to be incident onto a light reception surface of a charge coupled device (CCD), and an electrical detection signal corresponding to the light reception position is obtained. A signal processing circuit processes this detection signal on the basis of a geometric positional relationship between the light reception position detected and the pin-hole so as to detect the position of the sun.
Using such a sensor, the air conditioner mounted in a car can correct the air conditioning condition with good balance inside the car on the basis of the detection data of the position of the sun, that is, its direction and altitude. Consequently, comfort inside the air-conditioning space can be improved.
An insolation sensor for use in air conditioning must determine a substantial center position of the insolation of the solar rays in accordance with the change of weather conditions but not the actual position of the sun. In other words, the insolation from the sun received on the ground includes not only direct rays but also scattered rays due to clouds, etc., in the sky. Among these, the direct rays come from a direction corresponding to the actual position of the sun, but the scattered rays come from many directions irrespective of the position of the sun.
Accordingly, when the weather is fine with hardly any clouds in the sky, the quantity of the scattered solar rays becomes small. In other words, the components of the direct rays are predominant and the components of the scattered rays are so small that they can be substantially neglected. As the quantity of clouds becomes greater, however, the intensity of the components of the direct rays becomes lower, while the components of the scattered rays become greater. Accordingly, a case occurs where the main direction of insolation from the sun is different from the actual direction of the sun in accordance with the weather conditions. On the other hand, the air conditioning condition inside the car is affected not only by the direct rays of the sun but also by the scattered rays as they both raise the internal temperature of the car. For this reason, it is of importance in air conditioning control to detect the direction of the main insolation.
However, the prior art structure described above is not yet free from the following drawbacks. FIG. 21(a) of the accompanying drawings shows the detection principle using a CCD 21, and an explanation will be given briefly of the case of unidirectional detection. A light shading film 23 is disposed on a light reception surface 22 of the CCD 21 with a predetermined gap between them, and a pin-hole 24 is bored at a position of this light shading film 23 corresponding to the center of the light reception surface 22. When the CCD 21 receives a beam incident through the pin-hole 24 on the light reception surface 22, a charge is stored at the light reception position. The charge thus stored in the CCD 21 is taken out as an electrical signal corresponding to the light reception position by a signal processing circuit, and this circuit outputs a digital signal of an "H" level or an "L" level depending on whether or not this electrical signal is above a predetermined level.
When the weather is fine and the solar rays are received at this time, the intensity of the direct rays is high. Accordingly, the distribution state of the rays received by and obtained from the light reception surface 22 of the CCD 21 can be obtained as the detection signal relying almost solely on the direct rays. Accordingly, the incident direction of the solar rays can be detected as the center position of the detection signal.
When clouds exist in the sky and the weather is cloudy, the solar rays reaching the ground consist almost solely of the scattered solar rays. Accordingly, the scattered rays are incident to the position immediately below the pin-hole 24 on the light reception surface 22 of the CCD 21. In this case, since the ground substantially receives the scattered rays of the solar rays, the insolation direction can be detected from the center position of the scattered rays. See FIG. 21(d).
When the quantity of clouds is not so great and the weather is slightly cloudy, the scattered rays are incident with a certain insolation intensity into the CCD 21 together with the direct solar rays. In this case, the direct rays are incident into the position of the light reception surface 22 of the CCD 21 in accordance with the direction of the sun, while the scattered rays are incident into the position immediately below the pin-hole 24. However, under the slightly cloudy condition, the intensity of the direct rays becomes weaker and the difference from the intensity of the scattered rays becomes small and cannot be neglected.
Accordingly, if the direct rays and scattered rays of the solar rays are incident into the light reception surface 22 of the CCD 21 when the weather is slightly cloudy, a light reception detection signal is output in a region shown in FIG. 21(c) in accordance with the light reception intensities. As a result, when the center position of the light reception position is determined from the light reception signal obtained as a digital signal, the resulting center position is greatly deviated from the actual light reception center of the direct rays as well as from the actual insolation direction.
As described above, the prior art structure detects the position of received solar rays from a digital signal using the CCD 21. Accordingly, it fails to detect not only the position of the sun but also the substantial insolation direction in accordance with the change of the weather condition, and when the detection result is used for insolation correction in air conditioning control, the detection data of the insolation quantity and the insolation direction cannot enable accurate correction processing.